Introducing the free C-V2X workbench
2026-10-12, by ITS Roads
What each tool on cv2x.itsroads.com does, who it is for, what it is not for, and how to tell us what to build next.
ITS Roads, LLC has put a set of free, browser-based tools for SAE J2735 connected-vehicle messages at cv2x.itsroads.com. This post explains what is there, who we built it for, and the limits you should know about before you use any of it.
Why we built it
Agencies standing up a C-V2X pilot, integrators configuring their first roadside units, students learning the standards and researchers working with captured data all run into the same wall: the messages are binary (ASN.1 UPER), the standard is licensed, and the tools that open the messages are either expensive, tied to one vendor, or scattered across command-line projects. Most people end up reading hex by hand or trusting whatever their vendor's utility prints.
We work on these deployments for a living. The workbench is the set of tools we wished we had on the first project, offered free so that the next agency starts further along.
What each tool does
Decoder. Paste hex, base64, XER or JSON and get the message back as a summary table, a map (for anything with a position) and a JSON tree. Whole Ethernet frames, WSMP headers and IEEE 1609.2 signed data are peeled off automatically. The decoder tries the 2024 revision of J2735 first and falls back to 2020 and 2016, and tells you which one worked. Every field has a help affordance that explains its meaning, units and range.
Creator. Start from a validated template (BSM, SPaT, MAP, TIM, PSM, SRM, SSM, RSM, SDSM, EVA and more) or paste your own JSON, edit it, and encode it with constraint checking. You get UPER hex, base64, COER and XER, and the same summary view the decoder shows, so you can confirm the message says what you meant.
Map builder. Draw intersection lanes on an aerial map, set their attributes and connections, and get a MAP message with correct centimeter node offsets and signal groups. Draw a TIM or RSM region for a work zone, a curve or a speed advisory. Draw a corridor once and generate a numbered batch of TIMs or RSMs, one per segment. The builder can also produce a SPaT that matches the MAP's signal groups, so the two can be tested together.
Live feeds. Point an RSU's received-message forwarding at a UDP port here and watch what it hears: vehicles from BSMs with breadcrumb trails, pedestrians from PSMs, MAP lanes colored by SPaT state, signal-priority requests and responses. Record, replay and export. A simulated demo corridor runs all the time so there is always something to look at.
Simulator. Build an intersection, a work zone or a TIM corridor step by step, with a ring-barrier controller, RSUs and equipped vehicles, then run it and read the real J2735 bytes as they flow. It is a training tool: it shows what each piece of equipment contributes and what the driver would see.
Wiki. Plain-language guides to each message, to how SPaT and MAP work together, to signal priority, SCMS, FCC licensing, NTCIP 1218 and TMC integration. Written in our own words; we do not reproduce the standard.
API. Everything the decoder and creator do is available as a JSON API with a free daily quota, so scripts and course material can call it directly.
RSU registry and push. With a free account you can register your roadside units and push a message to them over NTCIP 1218 store-and-repeat or immediate forward. Credentials are stored encrypted and never leave your account.
Who it is for
Agency traffic and ITS engineers who need to check what a vendor delivered. Integrators who need a second opinion on a MAP before it goes on the RSU. Students and instructors who want to see the bytes behind the diagrams. Researchers who need captured BSM data decoded into something a spreadsheet can read. If you are one of these people, you do not need to install anything or pay anything.
What it is not for
This is a research, education, testing and pilot-planning tool. Messages produced here must not be used in safety-critical applications or broadcast on public roads until your agency has reviewed them, validated them against the standard with tooling it trusts, and run them through the RSU or controller vendor's conformance process. The codec checks ASN.1 constraints; it does not know whether a lane exists or whether a signal group matches the controller. There is no warranty, data may be incomplete or wrong, and ITS Roads is not affiliated with SAE, IEEE, NTCIP, NEMA or USDOT. The J2735 standard itself is licensed from SAE and is not redistributed here. The full text is on the disclaimer page, and a short version appears on every tool page.
Tell us what to build next
More message types, fields, datasets and workflows will be added over time, and the order is set by what people ask for. The feedback page takes a name and email (both optional) and a short message. Requests from agencies standing up pilots go first.
If you need the work done rather than the tool, ITS Roads plans and builds connected-vehicle deployments for agencies: MAP and SPaT authoring and validation, RSU configuration and monitoring, and pilot planning end to end.
Research and training tool. Not for safety-critical use. Read the disclaimer. Questions or requests: tell us what you want to see.